Numerous business applications require very large databases for storing information used in the business on a continuous basis. Database storage requirements may exceed 100s or 1,000s of gigabytes of data. Data storage costs generally limit such large databases to being stored on magnetic tape which presently offers the lowest data storage costs. Speed and reliability are important considerations, intensified by the relatively frequent access to the information stored within the database. However, tape storage generally requires the longest access time for retrieving the stored data. For example, once a tape is loaded onto a tape drive, accessing the data stored on the loaded tape is substantially slower than accessing data stored on a direct storage access device (DASD) or an optical disk. An even more substantial delay involves the time required to locate and mount the requested tape.
Automated storage libraries offer improved speed and reliability for storing and retrieving data stored on storage media, including magnetic tape. Early magnetic tape databases required an operator to retrieve a tape from a shelf and load the tape on a tape drive. This was very slow and prone to operator mistakes. Also, early magnetic tape reels were relatively large, i.e., 10.5 inch diameter ,reel furthermore, only 9 tracks were available for writing data to the tape. Correspondingly large areas were necessary to store the many required 10.5 inch magnetic tapes. Newer magnetic tapes are protected by a cartridge housing, and are substantially smaller than the 10.5 inch reels. Additionally, data can now be written to 18 tracks or more. Hence, each magnetic tape cartridge can store many times more data than the older reels. The advances made in magnetic tape technology have made automated cartridge libraries more effective since smaller areas are required to store more data on lighter weight cartridges.
Access time and reliability is improved by automatically managing the storage and retrieval of tape cartridges. Automated cartridge libraries include a plurality of storage slots for storing library resident tape cartridges, a robotic picker mechanism, and one or more tape drives. The robotic picker operates on command to transfer a tape cartridge between a storage slot and a tape drive within seconds. Operational benefits of using an automated cartridge library include: greater reliability in tape cartridge mounts; better predictability in request-to-mount time; and improved off-shift availability. An input/output port is also provided on the automated cartridge library for inserting and exiting cartridges from the library.
The robotic picker typically includes either a picker or a robotic arm having a vision system and a gripper system mounted thereon. The vision system can view a label attached to a tape cartridge to verify a correct tape cartridge is being picked by the gripper system. The vision system may also provide feedback to the gripper system so that the gripper system moves to the correct position to properly pick the identified tape cartridge. Both reliability and speed can be further improved by providing dual gripper/vision assemblies mounted on the single robotic picker. Reliability is improved since a failed gripper or vision system is backed by the second gripper or vision system. Speed is improved because pick-before-place operations can be performed if dual gripper/vision assemblies are available. In a pick-before-place operation, the robotic picker moves to a desired storage slot and the first gripper/vision assembly picks a cartridge from that storage slot. Next the robotic picker moves to a tape drive and the second gripper/vision assembly removes another cartridge from the tape drive so that the picked cartridge can be inserted into the tape drive.
In an automated cartridge library having a single gripper/vision assembly, if either the camera or gripper fails, access to data is interrupted until the failing unit is repaired or replaced. If the gripper/vision assembly is an integrated unit, a failure of either requires replacing the entire assembly. In an automated cartridge library using dual integrated gripper/vision assemblies, if either a camera or a gripper fails, there is no interruption in accessing tape cartridges, but pick-before-place operations will no longer be possible, thereby increasing data access times. Furthermore, should a camera or gripper of a first gripper/vision assembly fail, and a second camera or gripper of the second gripper/vision assembly fail, further access to data will be completely halted until repairs or replacements can be made.
Several robots have been disclosed having dual grippers for improving speed and reliability. Barrows, in U.S. Pat. No. 4,626,013, describes a robot arm having dual grippers mounted on a rotatable wrist. The first gripper is perpendicular to the second gripper such that, by turning the wrist ninety degrees, the first and second grippers interchange positions. Sugino, et al., disclose a robotic arm having dual grippers attached to a rotatable plate in U.S. Pat. No. 4,505,636. The dual grippers are mounted perpendicular to the plate such that when the plate is rotated 180 degrees, the second gripper will be in the same position previously occupied by the first gripper. Both U.S. Pat. Nos. 4,626,013 and 4,505,636 teach mounting dual grippers in a single assembly having interchangeable positions for increasing efficiency and speed. Neither reference suggests using a vision system operating independently with each gripper.
A robot having dual gripper/vision assemblies is described in German Patent 257,786. Each gripper/vision assembly is mounted on a robotic arm such that each gripper is guided by a dedicated camera. Thus, if either camera fails, the associated gripper becomes non-functional also. A robot having dual grippers and a single vision system is described by Suzuki in U.S Pat. No. 4,835,450. Each gripper is mounted on a robotic arm to grip and assemble parts brought to the robot on a conveyer belt. The dual grippers are provided for assembly requirements and not for speed or reliability. A failing gripper causes the robot to stop until repairs can be made. Furthermore, the vision system is mounted away from the robotic arms to provide vision functions simultaneously for the grippers while parts are manipulated.
A dual gripper/vision assembly for use in an automated cartridge library is set forth in U.S. Pat. No. 4,932,826 by Moy, et al. Moy, et al., describe a robotic arm having a turntable attached for mounting first and second gripper/vision assemblies thereon. The first gripper/vision assembly is located adjacent to the second gripper/vision assembly but pointed in an opposite direction. Therefore, the first gripper/vision assembly may access tape cartridges in an inner wall while the second gripper/vision assembly may access tape cartridges stored in an outer wall. The turntable rotates such that a 180 degree rotation places the first gripper/vision assembly in the position previously occupied by the second gripper/vision assembly. Each gripper/vision assembly is mounted at an angle of approximately 10 degrees for picking and storing tape cartridges. Each gripper is able to roll independently of its associated camera for picking a tape cartridge from a storage slot in one position or placing that tape cartridge in a tape drive in a another position. The independent rolling ability is necessary since each vision system projects an image for storing, retrieving, and placing tape cartridges to provide feedback for fine positioning of the robotic arm. As a result, each gripper requires a dedicated vision system. If either vision system fails, pick-before-place operations are no longer possible. Also, if either a camera or gripper of the first gripper/vision assembly fails, and either a camera or gripper of the second gripper/vision assembly fails, the automated cartridge library storage and retrieval functions are interrupted until repairs can be made. Wolfe, in U.S. Pat. No. 4,908,777, describes the calibration techniques used with the apparatus taught by Moy et al. Calibration requires fine tuning at each storage slot requiring each camera to operate simultaneously with each gripper.
What is needed is a robotic picker having a gripper/vision assembly wherein a single camera can operate independently with either of two grippers. This allows pick-before-place operations to be performed with the single camera. Furthermore, if either gripper fails, data access may continue with the remaining single gripper and camera. Reliability is further improved by adding a second camera which also operates with either gripper such that if both a camera and a gripper fail, in any combination, data access may continue.